High-throughput assays for screening potential inhibitors of proteases are known. An example of such an assay is the scintillation proximity assay (SPA). SPA technology involves the use of beads coated with scintillant. Bound to the beads are acceptor molecules such as antibodies, receptors or enzyme substrates which interact with ligands or enzymes in a reversible manner.
For a typical protease assay the substrate peptide is biotinylated at one end and the other end is radiolabelled with low energy emitters such as .sup.125 I or .sup.3 H. The labeled substrate is then incubated with the enzyme. Avidin coated SPA beads are then added which bind to the biotin. When the substrate peptide is cleaved by the protease, the radioactive emitter is no longer in proximity to the scintillant bead and no light emission takes place. Inhibitors of the protease will leave the substrate intact and can be identified by the resulting light emission which takes place in their presence.
The SPA assay works well. However, labeling of the substrate could result in inactivation of the substrate. In addition, radiolabeled emitters may pose both health and environmental concern. Therefore there is a need for producing a high-throughput assay which does not require the use of radioactive substances.